Unibit with replacement blade

ABSTRACT

A unibit with replacement blade provides economical refreshing of the many cutting facets of a unibit drill bit with a unibit replacement blade that is releasably secured in the unibit body. In one aspect of the invention, a replacement blade with cutting edges on one or both opposite side edges is releasably locked into the unibit body by a transverse locking screw. The blade can be provided with an integral tip drill when desired. In another aspect of the invention, one or more replacement blades is releasably secured in a recess in the unibit body with a simple blade lock mechanism, the blades being positioned symmetrically around the axis of the drill. In one embodiment, the blade lock is an eccentric cam member that rotates into and out of locking engagement with the blade. Other blade locks include clamping screws, screws through the blade, cam plates, tapered blades, and blade receiving grooves. Another aspect of the invention provides a replaceable tip drill.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application of co-pending U.S. patentapplication Ser. No. 11/430,458, entitled Unibit With Replacement Bladeand filed on May 9, 2006, by Scott C. Seeley, now co-pending, thedisclosure of which is incorporated here by reference.

BACKGROUND OF THE INVENTION

The invention relates generally to hole drilling bits that are used todrill holes in sheet metal and other sheet materials. More specifically,the invention relates to a stepped multiple hole size drill bit, whichis commonly known as a unibit or step drill. Unibits are relatively moreexpensive than single size twist drills and tend to be used frequentlybecause of their versatility of being capable of drilling a variety ofhole sizes. This frequent use also causes them to have a relativelyshort life. Further, unibits are typically not re-sharpened when wornbecause of the level of effort and expense to sharpen their many cuttingfacets.

One object of the present invention is to provide a unibit that caneconomically be resharpened by means of one or more easily replaceableblades.

BRIEF SUMMARY OF THE INVENTION

Accordingly, a unibit with a replacement blade of the invention provideseconomical refreshing of the many cutting facets of a unibit with aunibit body and replacement blade that is releasably secured to theunibit body by a blade lock without a complicated mechanism. In onepreferred embodiment of the invention, a single replacement blade havingcutting edges on one or both opposite side edges is secured in a slot ina conical head of a body then are threaded by screws that extend throughthe body on one side of the slot, then through an opening in thereplacement blade, and into the second side of the body the blade can beprovided with or without an integral tip drill. The conical head canhave straight or stepped sides. In another embodiment of the invention,one or more replacement blades having cutting edges on one side arelocked in blade retaining recesses formed in the conical head of theunibit body. The blade lock can be an eccentric cam member that rotatesinto and out of locking engagement with the blade. In other embodimentsof the invention, other types of novel blade locks are employed to lockthe replacement blade in place. Another aspect of the invention providesa replaceable tip drill and a fastener that urges the tip drill into aseated position in the unibit body. The unibit of the invention may beprovided with one or more replaceable blades.

These and other features or benefits of the invention will be recognizedfrom this specification, including the claims and the drawing figures,by one having ordinary skill in the art and by those who practice theinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an exploded side elevation view of a first alternativeembodiment of a unibit with replacement blade of the invention;

FIG. 2 is a top plan view of a replacement blade thereof, along lineII-II of FIG. 1;

FIG. 3 is a bottom plan view thereof,

FIG. 4 is a top plan view of a body of the unibit with replacement bladeof FIG. 1;

FIG. 5 is an end view of the embodiment of FIG. 1;

FIG. 6 is an end view of a second alternative embodiment thereof,

FIG. 7 is an end view of a third alternative embodiment thereof,

FIG. 8 is an end view of a fourth alternative embodiment thereof,

FIG. 9 is an end view of a fifth alternative embodiment thereof,

FIG. 10 is a perspective view of a sixth alternative embodiment of aunibit with replacement blade of the invention;

FIG. 11 is a plan view thereof;

FIG. 12 is a side elevation view thereof,

FIG. 13 is an end view thereof, taken from the tip end thereof,

FIG. 14 is a side elevation view of a seventh alternative embodiment ofa unibit with replacement blade of the invention;

FIG. 14 a is an enlarged fragmentary view of an edge thereof, showing anundercut at a junction between successive steps of a body thereof,

FIG. 15 is a plan view of the embodiment of FIG. 14;

FIG. 16 is a side elevation view of a clamping screw thereof,

FIG. 17 is ahead end view thereof;

FIG. 18 is a tip end perspective view of a replacement blade of theembodiment of FIG. 14;

FIG. 19 is a side elevation view thereof,

FIG. 20 is an edge view thereof,

FIG. 21 is a cross section view thereof, taken along line XXI-XXI ofFIG. 19;

FIG. 22 is a side elevation view of the tip drill of the embodiment ofFIG. 14;

FIG. 23 is a plan view of the tip drill of FIG. 22;

FIG. 24 is an end view of the tip drill of FIG. 22;

FIG. 25 is a perspective view of one preferred embodiment of a unibitwith replacement blade of the invention;

FIG. 26 is an exploded perspective view of the embodiment of FIG. 25;

FIG. 27 is a plan view of the unibit of FIG. 25;

FIG. 28 is an end view of the embodiment of FIG. 25, taken from the tipor left end as shown in FIG. 27;

FIG. 29 is an end view of the embodiment of FIG. 25, taken from theshaft or right end as shown in FIG. 27;

FIG. 30 is a cross-sectional view of the embodiment of FIG. 25 takenalong line XXX-XXX of FIG. 27;

FIG. 31 is perspective view of the replacement blade of FIG. 25;

FIG. 32 is a plan view of the replacement blade of FIG. 31;

FIG. 33 is an edge view of the replacement blade of FIG. 31;

FIG. 34 is a cross-sectional view of the replacement blade of FIG. 31,taken along line XXXIV-XXXIV of FIG. 32; and

FIG. 35 is an end view of the replacement blade of FIG. 31, taken fromthe tip or left end as shown in FIG. 31.

DETAILED DESCRIPTION OF THE INVENTION

With general reference to the drawing figures, a first embodiment of aunibit with a replacement blade according to the invention 20 has atleast a body 22, a replacement blade 24 (sometimes referred to as areplaceable blade), and a blade lock 26. The body is a body of rotationabout an axis “A” and has two opposing ends 27 and 29 (FIG. 4). A shaftportion 28 extends from one end 29 (first end) toward the opposing end27 (second end) and a generally conical head 30 extends from theopposing end 27 toward the shaft. The head 30 includes a tip 31 at end27 and a base 33 that joins the shaft 28. The base can have an enlargedrim 35 that restrains the head from passing entirely through a drilledhole in sheet material. The enlarged rim is optional and may not beemployed in all cases. In the first embodiment, the head 30 has aninclined outer surface 37 that includes a series of steps 32 ofprogressively increasing diameter and a series of ramps 34 interposedbetween and connecting adjacent steps. While the steps and ramps in thehead do not have cutting edges, they improve the fit and orientation ofthe unibit in the drilled hold in the panel or sheet material beingdrilled and improve the drilling action.

The shaft 28 is adapted to be secured into a rotating machine, such as adrill or the like (not shown). For example, the unibit 20 may be usedwith one-quarter inch, one half inch or other sizes of drills and thelike. Thus, the shaft may be sized accordingly and in consideration oftorque loading on the head 30, as is understood by one having ordinaryskill in the art. The body 22 may be made of any appropriate cuttingtool holding or foundation material, such as 4140 or 6150 steel, with4140 steel being less hard and generally less expensive. Other types ofsteel or alloys will work. Unlike conventionally known unibits, whichhave a cutting edge integral with their body, the cutting edge of theunibit according to the invention is incorporated in a separatereplacement blade. Thus, the body does not need to be formed of the samehardened cutting tool material as the blades and their cutting edges.This can reduce the cost of the tool significantly.

In the first embodiment, a blade receiving recess 40 is formed in eachside of the head 30 and releasably receives a corresponding replacementblade 24. As shown in the drawings, the blade receiving recess is agenerally V-shaped sectional void in the head 30 that resembles aquarter-section-like portion from the head. This is not a truequarter-section, however, in that the sides or walls 42 and 48 of thesection are not aligned (coplanar) with the axis of rotation “A.”Rather, as shown in the end view of the FIG. 5, the plane of side 48 isoverextended beyond the axis. The extent of overextension is preferablyabout the thickness of the replacement blade 24, such that a cuttingedge 46 of the replacement blade at a face surface 54 of the blade liesin a plane that extends generally through the axis “A.”

The replacement blade 24 is a generally triangular shaped plate memberthat is constructed of a suitably hard material, such as 6264 toolsteel, for example. In the first embodiment, the blade has two long legs44 and 45 and a short leg 47. One of the long legs 44 forms an inclinedouter edge of the blade. This leg has a stepped cutting edge 46 that isdefined by a series of flats 50 and ramps 52. In use, the head and bladewill be rotated and the blade cutting edge will be along a leading faceor surface 54 of the blade, relative to the direction of rotation.

The flats 50 are generally parallel with the reference axis “A” when theblade 24 is installed in the head 30, and are spaced a progressivelyincreasing distance from the axis. Again, as with the steppedconfiguration of the head, the ramps 52 of the replacement blade extendbetween adjacent flats. The flats 50 and ramps 52 of the bladecorrespond to the steps 32 and ramps 34 of the head but extend slightlyradially outward from the head 30. Thus, the cutting edge is exposed todo its job of cutting, while the head is a foundation for the blade andholds and positions the blade.

The blade lock 26 releasably secures the blade 24 in the receivingrecess 40 and is configured in the first embodiment of the invention asan eccentric cam 59 rotatably mounted in the blade receiving recess 40of the head 30. The blade lock 26 has an eccentric cam head 60 on apivot shaft 62. The shaft extends into a corresponding hole in the head.Preferably, the shaft and the hole are provided with cooperating screwthreads that engage in forced fit. Thus, disengagement or removal of theblade lock from the head in use is resisted by the force fit engagementof the shaft with the head and their screw threading.

Another feature of the first embodiment of the invention is that aninner end 63 of the blade receiving recess 40 in the head 30 of theunibit is curved outwardly. This curved end directs metal shavingsradially outwardly from the tool and prevents shavings from collectingin the recess.

In a second embodiment of the invention, shown in FIG. 6, rather thanlocking the blade in place with the eccentric cam 60 of FIG. 1, theblade can be locked in place by a blade lock 26′ that includes a camplate in the form of angle plate 71 that bears against the outside ofthe blade. A bolt 73 extends through a slot 72 in the angle plate andscrews into a threaded, inclined opening 75 in the body of the unibit.Tightening the bolt urges the bolt against an inclined outer surface ofthe angle plate and causes the angle plate to clamp the blade inposition.

In a third embodiment of the invention, shown in FIG. 7, blade lock 26″includes a screw or bolt 77 that extends into a threaded opening 79 thatis parallel with the side of the blade. A cam plate 81 with an inclinedside is positioned between the blade and a screw head 83, so that thehead of the screw urges the plate against the blade as the screw isscrewed into the opening.

As an alternative to the use of a cam plate, the replacement bladeitself 85 can be formed with an inclined side 87, as shown in blade lock26′″ in FIG. 8. In this fourth embodiment, axial movement of screw 89into hole 90 causes the head 91 of the screw to engage the inclinedsurface and urge the blade into a locked position. The head of the screwcan be tapered to mate with the incline of the sides of the blade.

In a fifth embodiment of the invention, shown for exemplary purposes inFIG. 9, the blade receiving recess 40′ of the body of the unibit can beprovided with an elongated groove 93 that extends axially in wall 42adjacent wall 48. The groove receives an inner edge 45 of the blade andholds it in place while any of the blade locks clamp the blade inposition. The groove 93 for the blade lock is shown for illustrativepurposes in connection with the embodiment of FIG. 9. This groove alsocan be used, however, for other embodiments.

Another feature of the previous embodiments of the invention is areplaceable tip drill 64 that is releasably mounted in the tip of theunibit. The tip drill 64 may be provided either in combination with aunibit having a replacement blade feature, or in a unibit having afixed, non-replacement blade. Tip drill 64 includes a shaft 66 that issecurely and releasably received in a cooperating shaft receptacle 68 inthe tip 31 of the unibit head 30. A set screw 70 or the like may be usedto secure the tip drill to the unibit head. Other means fornon-rotatably securing the tip drill in the head can be employed,including a mating non-circular (e.g., square) shaft and receptacle. Thetip drill is formed of a cutting tool material, such as 6240 steel. Thetip drill has a sharpened drill point 80 for starting a drill hole.Desirably, the tip drill also has at least one drill step comprising aramp 82 and a flat 84 at an increased diameter that mates with thesmallest diameter flats and ramps at the top of the body. It should benoted that a tip drill is not necessarily employed in every case. Insome instances, such as when the bit is employed in sheet materialhaving a pre-formed hole, the bit might not employ a tip drill at all.

The unibit 20 has at least one replacement blade according to theinventive concept. As shown in FIG. 1, a second replacement bladepreferably is provided in the first embodiment in a generallydiametrically opposed and rotationally balanced position. One havingordinary skill in the art may identify uses and situations where morethan two blades is desired, in which case the blades are disposedsymmetrically around the head.

A sixth embodiment of the present invention is shown in FIGS. 10-13. Inthis embodiment, as in the previous embodiment, unibit 100 includes abody 102, a replacement blade 104, and a blade lock. The blade lockincludes a screw 106 positioned adjacent to the replacement blade 104that extends parallel to or preferably at a slight inward angle towardthe replacement blade. The blade lock also includes a screw 108 thatextends through an opening 110 in the heel 128 of the blade. The unibit100 (also called a step drill) can include an enlarged rim 112 at thebase 113 of the conical head 111 to prevent the drill from passing allthe way through an opening in sheet material. The enlarged rim isoptional and may not be employed in all circumstances. A mounting shaft114 extends axially from the base 113 of the head 111. Shaft 114 hasflattened portions 116 spaced around the shaft to prevent the shaft fromrotating in the driver. The drill includes a replaceable drill tip 118having a stepped conical head 120 mounted on a shaft 122 that extendsinto an opening in the end of the drill. Shaft 122 has a flattenedsurface that faces set screw 124, which is threaded in opening 126adjacent the end of the drill. Set screw 124 holds the tip drill inplace.

The primary difference between the drill in FIGS. 10-13 and the drill ofFIG. 1 is the manner in which the replacement blade is mounted to thehead of the drill. Screw 106 is similar to screw 60 in FIG. 1, exceptthat it does not require an eccentric outer surface as in FIG. 1.Preferably, screw 106 is at a slight angle with respect to the surfaceof the blade, and the head of the screw has a slightly tapered surface(similar to FIGS. 7-9).

The screw thus tightens against the sides of the blade as it is advancedinwardly into the tapered screw hole. Another distinctive feature of theembodiment of FIGS. 10-13 is that screw 108 firmly retains the heel 128of the blade in place. Screw 108 has a head with a tapered outer surfacethat mates with a tapered surface in opening 110 so that screw 108 canbe countersunk into the opening and still clamp the heel of the blade tothe body of the unibit. A screw having a head larger than the openingthrough which the screw fits also would serve the same clamping purpose,although a protruding screw head could have the disadvantage ofimpairing somewhat the discharge of shavings from the drill bit. The useof the additional clamping screw 108 more securely attaches thereplacement blade in place in the body of the unibit.

In order to provide an even more secure attachment of the replacementblade to the body of the unibit, the recess in which the blade of FIG.10 is mounted can have a groove 130 formed therein in which the adjacentedge of the unibit fits, in the manner of groove 93 in FIG. 9.

The blade formed in the foregoing manner provides a more secureattachment for the replacement blade than that described in the firstsix embodiments. This embodiment may therefore be preferred for at leastsome applications where one of the first six embodiments is used.

A seventh embodiment 200 of the present invention is shown in FIGS.14-24. Unibit 200 includes a body 202 and a replacement blade 204. Thebody includes a shaft 208 at one end 209 and a conical head 210 at asecond end 207 of the body, all as in the prior embodiments. The outersurface of head 210 includes a plurality of steps 212 progressivelyincreasing in diameter and a series of ramps 214 interposed between theadjacent steps.

Shaft 208 includes flattened portions 216 spaced around the periphery ofthe shaft for non-rotatably mounting the shaft in a driver chuck.

The head 210 of the body is similar to the previous embodiment exceptthat a small undercut portion 217 is formed between the adjacent stepsand ramps of each step in the drill, as shown in FIG. 14 a. In a typicaldrill having a maximum outer diameter of about 1 inch, the undercut maybe approximately 0.008 inches deep.

Replacement blade 204 is constructed in a manner similar to replacementblade 104 of FIGS. 10-13, except that the heel 220 of the blade includesa slot 222 instead of a hole. A screw 224 extends through the slot intoa threaded opening in the head of the drill body. The slot makes itpossible to adjust blade position or replace a blade simply by looseningthe screw and sliding the blade out of the slot instead of having toremove the screw 224 completely from the body.

Another feature of replacement blade 204 is that the blade includes agroove 226 adjacent and parallel to the leading edge of the blade. Thisgroove improves the operation of the blade.

The replacement blade 204 is held in position by means of clamping screw228, shown in FIGS. 16 and 17. In an exemplary embodiment, screw 228includes a threaded shank 230, which is about 0.13 inches in diameterand 0.22 inches long. A beveled collar 232 is formed at an angle ofabout 30 degrees from the axis of the screw. A cylindrical band 234having a diameter of about 0.26 inches adjoins the tapered collar, andan inwardly tapered outer end 236 is formed at the end of the screw. Ahex drive opening 238 is formed in the end of the screw for rotating thescrew.

The screw fits in a hole 239 having a tapered opening that mates withtapered collar 232. When the screw first enters the hole, the screwthreads permit some sideways movement of the screw in the hole but asthe screw advances further into the hole, the hole draws the screw intomore fixed axial alignment with the hole. When the tapered screw collarengages the tapered opening in the hole, the band on the screw isbrought tightly into holding engagement with the side of the blade.Thus, an out of round or cam type of screw connection is not required inthis embodiment. To further improve the blade holding power of thescrew, the hole can be at a slight angle, so that the collar on thescrew is brought into increasingly tight contact with the side of theblade as the screw is advanced into the hole.

Another feature of this embodiment is the tip drill 240 that fits in anopening 242 in the end of the drill. Tip drill 240 has a shank 244,which has an inclined locking surface 246 thereon. A set screw 248extends at an angle through a threaded hole in the body, such that anend of the set screw bears against the inclined locking surface andurges the shank of the tip drill axially inwardly into the opening inthe drill body so as to tighten the engagement of the tip drill in thedrill body as the set screw is tightened. The tip drill has a cuttingsurface and step on the outer end 250 thereof that mates with the stepsof the drill formed along the head of the drill body and the outer endof the replacement blade.

In operation, step drill 200 operates in the same manner as the previousembodiments.

The eighth embodiment 300 of the present invention is one of thepreferred embodiments, and is shown in FIGS. 25-35. Unibit 300 includesa body 302 and a replacement blade 304. The body includes a shaft 308 atone end 309 and a conical head 310 at a second end 307 of the body, allas in the prior embodiments. Conical head 310 has an inclined outersurface. In the illustrated embodiment, the outer surface is generallysmooth and straight. The outer surface, however, could have the stepsand flats of prior embodiments, such as steps and flats 32 and 34 of theFIG. 1 embodiment. Providing steps and flats in the body increases theexpense of the product and the unibit works without steps and flats inthe head. However, the steps and flats seem to improve the smoothness ofthe operation of the unibit by facilitating the orientation andadvancement of the unibit in the drilled hole and by reducing anytendency of the blade to bind in the hole.

Shaft 308 includes flattened portions 316 spaced around the periphery ofthe shaft for non-rotatably mounting the shaft in a driver chuck. Theunibit body 302 can include an enlarged rim 312 at a base 314 of theconical head 310 to prevent the drill from passing all the way throughan opening in sheet material. The enlarged rim is optional and may notbe employed in all circumstances.

Head 310 has an axially extending slot 355 therein that extendslaterally all the way through the cone substantially from the tip to thebase of the head and has open sides at the inclined surfaces on bothsides of the head. The head on both sides of the slot forms spaced bladesupport members 354, which are connected to one another and to the shaft308 at the base 314. Each blade support member is generally triangularin shape, having two long legs 356 and one short leg 358, and the bladesupport members are positioned so that the replacement blade can be slidinto the slot 355 between the blade support members. The long legs 356of each blade support member 354 are curved outwardly where the bladesupport member attaches to the base. This curved end 357 directs metalshavings radially outwardly from the tool. Where the long legs of eachprong join at the tip end 307, the prong tips 360 may be blunted toensure that a tip drill 306 on the blade extends beyond the head.

The replacement blade 304 is a generally triangular shaped plate memberthat is constructed of a suitably hard material, such as 6264 toolsteel, for example. In the eighth embodiment, the blade 304 can includean integral tip drill 306 at a tip end 309 of the blade and a base 314that is positioned adjacent the shaft 308. The blade 304 has two longlegs 318 and a short leg 320. The two long legs 318 join at the tipdrill 306, which is formed integrally with the blade when a tip drill isdesired. There are some instances where a tip drill is not desired, sothe blade also can be formed without a tip drill 306. In such a case,the blade ends at blunt end 309 as shown in phantom in FIG. 32. The tipdrill 306 has a sharpened drill point 352 for starting a drill hole.Each of the long legs 318 of the blade 304 forms an inclined outer edgeof the blade. Each of these legs 318 has a stepped cutting edge 322 thatis defined by a series of flats 324 and ramps 325. In use, the head 310and blade 304 will be rotated and the blade cutting edges 322 will bealong the leading face or surface 328 of the blade, relative to thedirection of rotation. Each cutting edge 322 of the replacement blade304 may include a groove 326 adjacent and parallel to the leading edgeof the blade. This groove improves the operation of the blade.

The blade 304 includes two aligned blade holes 344 that are generallypositioned along the axis of the blade and the blade holder body whenthe blade 304 is installed in the head 310. The blade holes 344 alignwith the head holes 342 when the blade is installed in the head. Thebase or short leg 320 of the blade 304 includes a slot 346 that isgenerally along the axis “A” when the blade is installed in the head. Apin 348 extends through and is wedged or otherwise secured in hole 350that extends through the conical head and the slot in the head of thedrill body to provide proper positioning of the replacement blade. Theslot also makes it easier to replace a blade simply by removing screws330 and sliding the blade 304 out of the head 310.

The flats 324 are generally parallel with the reference axis “A” whenthe blade 304 is installed in the head 310, and are spaced aprogressively increasing distance from the axis. The ramps 325 of thereplacement blade extend between adjacent flats. The tip drill 306,flats 324 and ramps 325 of the blade extend outward from the head 310.Thus, the cutting edges are exposed to do their job of cutting, whilethe head is a foundation for the blade and holds and positions theblade.

The replacement blade 304 is held in position by means of clampingscrews 330 (similar to FIGS. 16 and 17). In an exemplary embodiment,each screw 330 includes a threaded shank 332, which is about 0.13 inchesin diameter and is long enough to engage the threads of both holes 342without protruding beyond the body so as to interfere with or impair theshaving achieved by the blade. A beveled collar 334 is formed at anangle of about 30 degrees from the axis of the screw. A cylindrical band336 having a diameter of about 0.26 inches adjoins the beveled collar,and an inwardly tapered outer end 338 is formed at the end of the screw.A hex drive opening 340 is formed in the end of the screw for rotatingthe screw.

The screws 330 fit in holes 342. The screws 330 fit through the holes342 in the near side of the head, extend through blade holes 344 in theblade 304, and then are threaded into threaded holes 342 in the oppositeside of the head.

In operation, step drill 300, which is one of the preferred embodiments,operates in the substantially the same manner as the previousembodiments but provides simplified construction, an integral tip drill(when desired) and secured mounting.

One having ordinary skill in the art and those who practice theinvention will understand that various modifications and improvementsmay be made without departing from the disclosed inventive concept.Various relational terms, including left, right, front, back, top, andbottom, for example, are used in the detailed description of theinvention and in the claims only to convey relative positioning ofvarious elements of the claimed invention and are not otherwise used tolimit the scope of the invention.

1. A unibit with replacement blade comprising: a body of rotation havingan axis, the body including a generally conical head having a base and atip at opposite axial ends thereof and having an inclined outer surfaceextending between the base and the tip, the head further including amounting shaft extending axially from the base for mounting the unibitin a rotating tool; the head including an axially extending recess in atleast one side thereof, the recess being formed in the outer surface ofthe head and extending inwardly toward an interior of the head; areplacement blade that fits in the recess, the blade having a steppedcutting surface on at least one outer side that extends outwardly beyondthe outer surface of the conical head, such that the cutting surface ofthe blade engages edges of a hole in a work piece before the work pieceengages the head; and a blade lock that releasably holds the blade in asecure cutting position in the recess in the head.
 2. A unibit as inclaim 1 wherein: the recess comprises an axial slot extending laterallyall the way through the conical body such that the sides of the slot areopen at opposite sides of the inclined outer surface of the head; theblade fits in the slot and includes stepped cutting surfaces on at leastone of two opposite sides edges of the blade, the sides with steppedcutting surfaces protruding beyond the inclined surfaces of the body atthe sides of the body; and the blade lock comprises a fastener thatengages the blade and locks it in position in the body.
 3. A unibit asin claim 2 wherein: the blade lock fastener comprises at least onelocking screw that engages a threaded opening formed in the bodytransversely to the slot and extending from the inclined outer surfaceinto the slot, the locking screw engaging and locking the blade in theslot when the screw is threaded into the opening, the blade beingreleasable by axially withdrawing the screw from the slot.
 4. A unibitas in claim 2 wherein the blade includes stepped cutting surfaces onboth of the opposite side edges of the blade and both side edges extendoutwardly beyond the inclined surfaces on both opposite sides of thebody.
 5. A unibit as in claim 2 wherein cutting surfaces on the bladeextend all the way to a tip end of the blade, the cutting surfaces atthe tip serving as a tip drill to initiate a hole in material to bedrilled.
 6. A unibit as in claim 2 wherein the blade has a generallyflat tip end without tip drill cutting edges for initiating a hole inpreviously undrilled material.
 7. A unibit as in claim 1 wherein theblade lock comprises at least one fastener that extends through anopening in the body that extends transversely across the slot, the bladehaving a mating opening through which the fastener fits when the bladeis in a mounting position in the slot.
 8. A unibit as in claim 7 whereinthe blade lock includes at least two spaced fasteners that extendthrough spaced openings in the body and blade.
 9. A unibit as in claim 1wherein the blade lock comprises a threaded fastener that extends firstthrough an opening in the body on one side of the slot then through amating opening in the blade, and then engages a threaded opening in theconical body on the opposite side of the slot.
 10. A unibit as in claim9 wherein the fastener has a head that includes a conical surface on anunderside thereof, the conical surface engaging the opening in the bladeand serving to center the opening in the blade with respect to thefastener.
 11. A unibit as in claim 2 and further comprising stabilitymeans for enhancing the stability of the blade and proper positioning ofthe blade in the body, the stability means comprising a matingprojection and slot in the edge of the blade and interior of the handlerecess that properly positions the blade in the recess.
 12. A unibitwith replacement blade, comprising: a body of rotation having an axis,the body of rotation having first and second opposing ends, the bodyhaving a shaft extending along the axis toward a second end from thefirst end, the body having a head extending toward the first end fromthe second end, the head comprising two blade support members separatedby an axial slot, with the head having a tip at the second end and abase at an opposite end of the head; and a replacement blade releasablysecured in the slot, the blade having two inclined sides, with cuttingedges on at least one of the sides, the cutting edges including a seriesof steps and ramps of increasing diameter, the blade being secured inthe slot so the cutting edges extend beyond the body in a direction thatis radially outward from the axis.
 13. The unibit of claim 12 whereinthe replacement blade further includes a tip drill with a cutting tip atone end opposite the base.
 14. The unibit of claim 12 wherein thereplacement blade is releasably secured between the blade supportmembers with one or more screws mounted transversely in the body forengagement with the blade.